Microsoft's Joe Belfiore, above, is hinting that a major Windows Phone app will be released on Monday.

While the leak of Windows Blue has resulted in an immense amount of Microsoft-related news, the tease of a major app release for the company's smartphone operating system has quietly gone without much notice.

Microsoft's Joe Belfiore, manager of the Windows Phone team, today tweeted that a major app will be released on Monday. Apparently, however, no one told Belfiore that Windows Blue leaked, as he called today "a quiet day."

Today's kind of a quiet day.I think I said "this week" on Monday.Doesn't the week go Monday to Monday? :)

While Belfiore didn't give any hints about what he was teasing, two potential Windows Phone apps that have been in the headlines in recent months are an updated version of the Facebook app and an Instagram app.

Nokia has been the forefront of conversation about both potential apps, as the company is currently running a campaign for Instagram to release its photo-sharing app on Windows Phone and its CEO, Stephen Elop, told a customer that a new Facebook app "is definitely being worked on."

Update: Belfiore has tweeted some new information about the app's release, including that it comes from a third-party developer and will no longer release Monday.

Bad news: next-fun-app-release delayed a few days.Still coming, just not today (monday).Sorry!